Purification of crude titanium tetrachloride



United States Patent m 3,108,854 PURIFECATKGN (BF CRUDE TITANIUM TETRACHLORHDE Delmar B. Davis, Brigham City, Utah, assignor to Titanium Metals Corporation of America, New York, N.Y.,

a corporation of Delaware No Drawing. Filed Feb. 23, 1961, Ser, No. 90,915

6 Claims. (Cl. 2387) This invention relates to the purification of titanium tetrachloride and more particularly to a simple and economical process for purifying so-called crude titanium tetrachloride to render it suitable for the manufacture of titanium metal, pigments, and compounds.

Crude titanium tetrachloride is generally produced by chlorination of titaniferous iron ores or rutile, and is invariably contaminated by various impurities which are also chlorinated, or are carried over with the gaseous titanium tetrachloride from the chlorination furnace. These impurities include chlorides of metals, impurities in the ore, dust and other foreign materials suspended in the TiCl, vapor stream, as well as other impurities picked up during processing. Many of these impurities may be separated by distillation processes. Some compounds, however, particularly those of vanadium, such as VOCI because of lack of appreciable differences in boiling points between such impurities and T-iCl cannot be readily so separated.

A chemical treatment is therefore often employed to convert such impurities to insoluble or high boiling point compounds, in which form they may thereafter be more readily removed, and the TiCl thereby purified. Chemical treating agents heretofore proposed have included metallic copper, various salts and compounds, oils, carbonaceous organic compounds and reactive sulfides. Most of these treating agents, however, are relatively expensive. In' addition, methods proposed for operating the treating and purification processes have not been adapted for continuous or cyclic operation.

.An object of this invention is to provide an improved method for the purification of crude TiCl A further object of this invention is to provide an ehicient and economical method for purification of TiC1 A still further object of this invention is to provide a method for purification of TiCl, in which a relatively inexpensive treating agent is employed in an efficient cyclic process. These and other objects of this invention will be apparent from the following description thereof.

In its broadest aspects this invention contemplates a process for purifying crude TiCl, which contains vanadium oxytrichloride VOCI The process comprises admixing said crude TiCl, in vapor state at a temperature between 600 C. and 800 C. with hydrogen in amount between 0.01% and by Weight of said crude TiCl and separating solid and high boiling point impurities, and by-product HCl and excess hydrogen, from the resulting gas mixture to produce purified TiCl The amount of hydrogen employed is substantially in excess of the amount stoichio-metrically required to reduce the VOCl content of the crude TiCl, to VOCl and is at least thirty times such amount. The temperature employed, within the limits stated, is below that at which hydrogen will react to any appreciable extent with TiCl, to produce titanium lower chlorides TiCl, or TiCl The temperature at which hydrogen is reacted with the gaseous impure TiCL, is critical. Within the defined temperature range, that is, between 600 C. and 800 0., hydrogen if present in suflicient excess will reduce vanadium compounds such as VOCl to produce solid or high boiling point vanadium chloride compounds such than Patented Get. 29, 1963 as VOCI which may be readily separated from the TiCl The reduction reaction appears to be directly between hydrogen and the vanadium compounds and does not involve the formation of titanium lower chlorides. At temperatures below 600 C. the hydrogen will not react with sufiicient speed and efficiency to be practical, and above 800 C. the hydrogen will tend to react with the TiCL, to produce titanium lower chlorides.

The amount of hydrogen employed to contact the crude TiCl, in vapor state is also critical. It should be between about 0.01% and 10% by weight of the crude TiCl, treated, and should represent a substantial excess over that necessary to reduce the undesirable vanadium compounds. To provide advantageous reduction efii ciency the amount of hydrogen should be at least thirty times that stoichiometrically required to reduce the VOCl content of the crude 'liCl, to V061 and it will be found that when this excess of hydrogen is employed at the operating temperature described, advantageous efiiciency in reduction of VOCI is obtained without reaction with TiCl, to produce lower chlorides, and substantially recovery of the TiCL, is obtained. The larger percentages of hydrogen Will generally be employed when the crude TiCl, contains chlorine, ferric iron or other impurities which will independently react with, and use up, a portion of the hydrogen. Since the hydrogen is employed as such a large excess over that theoretically required, most economic and preferred operation of the process of this invention requires that the excess hydrogen be recovered and recycled to provide .an integrated process. The by-product of the reaction between hydrogen and vanadium chloride compounds will be HCl and this will be separated with excess hydrogen on condensation of the purified TiCl It is significant and important that theby-produot gas mixture containing both H01 and excess hydrogen may be recycled back to treat additional crude TiCh. The HCl content of the gas mixture appears 'to have no appreciable effect on the efliciency of the hydrogen portion to provide the desired purification action. The by-product' HCl and excess hydrogen gas mixture may be continuously recycled until substantial exhaustion of its hydrogen content. This, however, is not desirable in commercial. operation since the dilution of the residual hydrogen by large excesses of HCl involves handling of large volumes or gas containing only a minor proportion of the reactive constituent and is most often uneconomical. The HCl may be removed by refrigerating and separating the condensed HCl, or a continuous recycling process may provide for bleeding off a proportion of :the HCl and excess hydrogen mixture and replacing it with pure hydrogen. The amount bled off should be equivalent to the production of HCl in the purification reaction so that an approximate equilibrium in regard to HCl content is obtained in the circulating gas stream. This will provide efiicient recycling of a predominant portion of the excess hydrogen and also an HCl-hydrogen gas mixture of requgled reactivity and hydrogen content for treating crude Ti \After treatment of crude TiCL, with the required amount of hydrogen at a temperature between 600 C. and 800 0, according to this invent-ion, the resulting gas mixture will contain excess hydrogen, H01 byproduct, and reduced vanadium compounds either as solid suspended particles or as high boiling point gases which may be readily separated from the TiCL, by fractional coudensatio-n or distillation. In its simplest form, this invention contemplates condensing the entire gaseous mixture at this stage, which will separate lay-product HCl and excess hydrogen, and subsequently distilling the TiCl to separate the insolubles and higher boiling point conhigher boiling point constitutents produced by the hydroen treatment reaction will be effectively condensed and collected. During such operation the temperature of the hot gas mixture Will be reduced to the boiling point of TiCl and a portion of the TiCl vapor may be also condensed; however, the amount of cold liquid TiCl employed should be such that not more than a minor amount of the TiCl content of the gaseous mixture is condensed. Preferably none, or only an insignificant amount of condensation of the TiCl, occurs and the wash liquid may be recooled and recycled with, when necessary, separation, conveniently by distillation, of accumulated high boiling point impurities. If an appreciable portion of the TiCl in the mixed gases is condensed at this stage in the wash liquid it may be recovered as purified product by distillation and combined with that obtained by condensation of the residual gases TiCl The residual gaseous TiCl with the solid and high boiling point impurities removed by the TiCl wash as described, is then separately condensed, thereby separating byproduct HCl and excess hydrogen gas. This condensed TiCl purified product will be found to be water white and of adequate purity for the manufacture of titanium metal, pigments and compounds. The by-product HCl and excess hydrogen gas mixture may be recycled as hereinbefore described, and the separated high boiling point compounds discarded or treated for recovery of their constituents if this appears desirable.

TiCl is often manufactured by direct chlorination of a mixture of coke or carbon With either rutile, ilmenite or other titanium dioxide containing ore. The chlorination action is exothermic and the product gases containing TiCL; are discharged from the chlorination furnace at high temperature, often in the range from 600 to 800 C. Therefore, in the commercial practice of this invention, it may be advantageous to admix the crude TiCl with hydrogen directly as it comes from the chlorination furnace, thus saving the expense required to heat previously condensed crude TiCL; up to the required temperature. When operating according to this modification the higher percentages of hydrogen within the cited range are generally required since the TiCh-containing gases will be diluted with substantial amounts of carbon monoxide and carbon dioxide produced as hy-products from the chlorination reaction, as well as in some cases ferric chloride, free chlorine and other materials which will react with hydrogen and reduce the amount available for the desired reaction with vanadium impurities. Therefore, under these conditions hydrogen percentages by weight of from 1% to of the weight of the TiCL; will generally be found to be most effective. In addition, since the uncondensed gases containing HCl lay-product and excess hydrogen will also contain a relatively large proportion of carbon monoxide and carbon dioxide, recovery and recycling of the excess hydrogen will not ordinarily be feasible. This economic loss, however, may be offset by the gain resulting from treating the already hot gases coming directly from the chlorination furnace.

The following examples illustrate embodiments of the practice of this invention.

EXAMPLE 1 A batch of dark colored crude TiCL; containing 0.4% VOCl was heated in an electrically heated boiler to continuously produce a stream of TiCl vapor at about 700 C. The stream of TiCl vapor was led through a contact column and there admixed with sufiicient hydrogen to provide a mixture containing 0.25% hydrogen by weight,

which constituted about times the amount stoichiometrically required to reduce the 0.4% VOCl content of the crud-e TiCl, to VOCl The admixture was maintained at a temperature of about 700 C. during passage through the contact column. The gases were then led through a vertical water cooled tube and shell condenser to condense and collect the TiCl and other condensable impurities.

The condensate was then distilled, and the distillate, which was condensed in a water cooled tube and shell condenser, was a purified TiCL; product of water white color containing less han 0.008% VOC1 and suitable for production of titanium pigments, metal and compounds.

EXAMPLE 2 The hot gas mixture produced in a furnace by reacting chlorine with rutile and coke was employed as crude TiCl in the process of this example. The hot gas mixs ture contained TiCl chlorine in amount about 1% by weight of the TiCl about 0.3% VOCl and about 2% ferric chloride on the same basis, carbon monoxide and carbon dioxide produced as by-products of the chlorination reaction as well as dust, carbon and other incidental impurities. The hot gases, maintained at a temperature between 700 C. and 750 C. were admixed with hydrogen in amount of 5% by weight of their TiCl, content. This amount of hydrogen constituted at least several hundred times the amount stoichiometrically required to reduce the 0.3% V001 to VOCl and even after allowing for consumption of a proportion of the hydrogen by other hydrogen reducible impurities. The admixture was then condensed and the condensate distilled to produce a purified TiCL, product of quality similar to that produced in Example 1.

EXAMPLE 4 The same crude TiCl; as used in Example 1 was'vaporized and treated at a temperature of 650 C. and admixed with 1% by weight of hydrogen, which constituted about 400 times that amount s'toichiometrically re quired to reduce the 0.4% contained V001 to VOCl The hot gas admixture was then led into a tower where it was contacted with a spray of room temperature pre viously purified liquid TiCl the amount of liquid TiCl introduced being sulficient to reduce the gases to the condensation temperature of TiCl (about 136 C.) and to condense only an insignificant amount of the TiCl in the gas mixture. The liquid spray effectively washed the TiCl and removed high boiling point and solid materials including reduced vanadium compounds.

The vaporous residual TiCl which had been washed by the liquid TiCl spray, was separately condensed to provide a purified product of quality similar to that obtained by the process of Example 1. f

When purifying crude TiCL; to be used for production of metallic titanium the vanadium content must be reduced to a very small amount. Generally speaking'a residual V001 content of less than 0.01% is essential, and available and convenient analytical methods do not provide accurate measurements below about 0.008%. Analysis of a treated product showing less than 0.008% V001 will therefore indicate a TiCL; of purified grade suitable for production of titanium metal or titanium pigments and for other commercial purposes.

In order to determine and demonstrate the critical nature of the large excess of hydrogen necessary to accomplish the objects of this invention, a number of test runs were made, following the procedure of Example 1. These runs were all made using crude TiCL; containing an average of 0.22% VOCl at a temperature of 700 C. and the excess of hydrogen stoichiometrically required to reduce the VOCl content of the TiCl was varied from 1.4 to over 1000 times. The results, tabulated in Table 1 below, show that when employing over 30 times excess hydrogen, purification was excellent and a product V001 content of less than 0.008% was obtained in every case. When employing hydrogen in excess less than 30 times the stoichiometrically required amount, the desired purification could not be consistently obtained. It will be noted that the purity of the product grows generally poorer (that is, the residual VOCl content is higher) as the hydrogen excess is reduced. This trend is not uniform however, and therefore in order to obtain consistent and reliable purification the hydrogen excess should be at least 30 times theoretical or stoichiometric.

Table 1 H2 Excess, VOCla in TiCh, Run N0. times percent stoichlometric 1080 Less than 0.008 87 Less than 0.008 46 Less than 008 In order to check the necessary hydrogen excess at a temperature lower than the 700 C. used in the tests of Table 1, another group of runs was made at 650 C. using similar crude TiCl and operating procedure. The hydrogen excess was set for comparison slightly above 30 times stoichiometric and the results tabulated in Table 2 below were obtained.

The process of this invention has a significant advantage in that the hydrogen treating agent reacts directly with the undesirable vanadium impurities to reduce these to chlorides of lower valent state which may readily be separated by a subsequent distillation. It is significant that within the temperature range defined, the hydrogen admixed with the hot vaporous TiCl will not react therewith to produce titanium lower chlorides in the presence of more readily reduced compounds, e.g., V001 While titanium lower chlorides themselves may also act as efiective treating agents, the formation and later separation of any excess of titanium lower chlorides, and resulting loss of TiCL is avoided under the conditions described.

Thus, it is seen that the process of this invention employs a very large excess of hydrogen to provide eflioient reduction of VOCl to VOCl at a temperature below that at which hydrogen will react with the TiCl to produce lower chlorides. The reduction action of hydrogen is therefore not applied to the TiCL which could result in loss from side reactions, and recovery of this compound in pure form is substantially 100 percent. The comparatively large excess of hydrogen required for elli- 6 cient reaction is not detrimental, however, in view of the discovery that it will reduce the undesirable vanadium compounds atthe low temperature employed even when admixed with HCl which is produced as a by-product of the reduction reaction. Under these conditions it is practical to employ a large excess of hydrogen to obtain the desired treatment efliciency and the excess hydrogen may be recycled to produce an efficient integrated cyclic process. In order to avoid HCl build-up in the recycled gas mixture, a minor proportion generally of the order from 2% to 15% may be bled oil and replaced by pure hydrogen to result in a relatively constant cycled gas composition.

This application is a continuation-in-part of my copending application Serial No. 862,066, filed December 28, 1959, now abandoned, which is a continuation-in-part of my application Serial No. 709,786, filed January 20 8, and now abandoned.

I claim:

1. A process for purifying crude titanium tetrachloride, TiCl containing vanadium oxytrichloride, V001 which comprises; admixing said crude TiC1 in vapor state with hydrogen in an amount between 0.01% to 10% by weight of said crude TiCl such amount of hydrogen being at least thirty times that stoichiometrically required to reduce the VOCl contained in said TiCl, to VOCl at a temperature between 600 C. and 800 C. and below that temperature at which said hydrogen will reduce said TiCL, to produce titanium lower chlorides, and separating from the soproduced gaseous admixture, solid and high boiling point impurities, and by-product HCl and excess hydrogen, to provide a purified TiCl product.

2. A process for purifying crude titanium tetrachloride, TiCl containing vanadium oxytrichloride, VOCl which comprises; admixing said crude TiCl in vapor state with hydrogen in amount between 0.01% to 10% by weight of said crude TiCl such amount of hydrogen being at least thirty times that stoichiometrically required to reduce the VOCl contained in said TiCL, to VOCI at a temperature between 600 C. and 800 C. and below that temperature at which said hydrogen will reduce said TiCl to produce titanium lower chlorides, condensing TiCL, from the so-produced gaseous admixture, thereby separating by-product HCl and excess hydrogen, and distilling said TiCL, to produce purified TiCl 3. A process for purifying crude titanium tetrachloride, TiCl containing vanadium oxytrichloride, V001 which comprises; admixing said crude TiCL; in vapor state with hydrogen in amount between 0.01% to 10% by weight of said crude T-iCl such amount of hydrogen being at least thirty times that stoichiometrically required to reduce the VOCl contained in said TiCl, to VOCl at a temperature between 600 C. and 800 C. and below that temperature at which said hydrogen will reduce said T iCl to produce titanium lower chlorides, condensing 'IiCL, from the soproduced gaseous mixture, thereby separating by product HCl and excess hydrogen, and distilling said TiCL, to produce purified TiCL, and recycling and admixing said excess hydrogen with additional crude TiCl 4. A process for purifying crude titanium tetrachloride, TiCl containing vanadium oxytrichloride, VOCl which comprises; admixing said crude TiCl in vapor state with hydrogen in amount between 0.01% to 10% by weight of said crude TiCl such amount of hydrogen being at least thirty times that stoichiometrically required to reduce the V001 contained in said TiCL, to VOCl at a temperature between 600 C. and 800 C. and below that temperature at which said hydrogen will reduce said TiCL, to produce titanium lower chlorides, condensing TiCL, from the soproduced gaseous admixture. Thereby separatinga mixture of by-product HCl and excess hydrogen, distilling said condensed TiCL, to produce purified TiCl and recycling and admixing said mixture of by product HCl and excess hydrogen with additional crude TiCl 5. A process for purifying crude titanium tetrachloride,

TiCl containing vanadium oxytrichloride, VOC-l which comprises; admixing said crude TiCl in vapor state with hydrogen in amount between 0.01% to 10% 'by weight of said crude TiC1 such amount of hydrogen being at least thirty times that stoichiometrica-lly required to reduce the VOCI contained in said TiCl, to VOCI at a temperature between 600 C. and 800 C. and below that temperature at which said hydrogen will reduce said TiCL, to produce titanium lower chlorides, washing the so-produced gaseous admixture with a spray of cold liquid TiCl in amount to condense not more than a minor amount of the TiCL, in said gaseous admixture, and condensing TiCL; from the residual gas mixture to provide a purified TiClrproduct.

6. A process for purifying crude titanium tetrachloride, TiCl containing vanadium oxytrichloride, V001 which comprises; admixing said crude TiC1 in vapor state with hydrogen in amount between 0.01% to 10% by weight of said crude TiCl such amount of hydrogen being at least thirty times that stoichiometrically required to reduce the VOCl contained in said TiCl to VOCI at a temperature *between 600 C. and 800 C. and below that temperature at which said hydrogen will reduce said TiCl to produce titanium lower chlorides, washing the so produced gaseous admixture with a spray of cold liquid TiCL; in amount to condense not more than a minor amount of the TiCl in said gaseous admixture, distilling the wash liquid TiCl separately condensing T i01 from the residual gas mixture, and combining the distillate from the distilled wash liquid TiCl with the condensed TiCl from the residual gas mixture to produce a purified H01 product.

References Cited in the file of this patent UNITED STATES PATENTS Great Britain Nov. 7, 

1. A PROCESS FOR PURIFYING CRUDE TITANIUM TETRACHLORIDE, TICL4, CONTAINING VANADIUM OXYTRICHLORIDE, VOCL3, WHICH COMPRISES; ADMIXING SAID CRUDE TICL4 IN VAPOR STATE WITH HYDROGEN IN AN AMOUNT BETWEEN 0.01% TO 10% BY WEIGHT OF SAID CRUDE TICL4, SUCH AMOUNT OF HYDROGEN BEING AT LEAST THIRTY TIMES THAT STOICHIOMETRICALLY REQUIRED TO REDUCE THE VOCL3 CONTAINED IN SAID TICL4 TO VOCL2, AT A TEMPERATURE BETWEEN 600*C. AND 800*C. AND BELOW THAT TEMPERATURE AT WHICH SAID HYDROGEN WILL REDUCE SAID TICL4 TO PRODUCE TITANIUM LOWER CHLORIDES, AND SEPARATING FROM THE SOPRODUCED GASEOUS ADMIXTURE, SOLID AND HIGH BOILING POINT IMPURITIES, AND BY-PRODUCT HCL AND EXCESS HYDROGEN, TO PROVIDE A PURIFIED TICL4 PRODUCT. 